Pipe Pressure Drop & Velocity

Darcy-Weisbach pressure drop, fluid velocity and fitting equivalent length for steel, copper, aluminum and nylon piping.

Darcy-Weisbach pressure drop

Pipe Pressure Drop & Velocity calculations for darcy-weisbach pressure drop are computed deterministically from published formulas, so the same inputs always produce the same result and the same OAS-XXXX verification hash.

Fluid velocity limits

Pipe Pressure Drop & Velocity calculations for fluid velocity limits are computed deterministically from published formulas, so the same inputs always produce the same result and the same OAS-XXXX verification hash.

Fitting equivalent length

Pipe Pressure Drop & Velocity calculations for fitting equivalent length are computed deterministically from published formulas, so the same inputs always produce the same result and the same OAS-XXXX verification hash.

Engineering summary

Governing parameters for the Pipe Pressure Drop & Velocity silo.

Governing parameters and computed results for this calculation
Parameter Value
Materials covered Steel · copper · aluminum · nylon
Nominal sizes 1/4–4 in
Air velocity limit ≤ 30 ft/s
Hydraulic velocity limit ≤ 20 ft/s
Friction factor model Swamee-Jain (Colebrook)

Frequently asked questions

What velocity limit applies to compressed-air piping?
Keep compressed-air velocity at or below 30 ft/s and hydraulic velocity at or below 20 ft/s. Higher velocities raise pressure drop sharply and invite erosion, noise and water carry-over.
How do fittings affect pipe pressure drop?
Fittings add an equivalent length of straight pipe: L_eq = Σ (L/D)·D. A 90° elbow is about 30 diameters, a globe valve about 340 diameters, so a short run with many fittings can drop more pressure than the straight pipe.
Which friction factor model does the calculator use?
The calculator uses the Darcy-Weisbach equation with the Swamee-Jain explicit approximation of the Colebrook friction factor, valid across laminar and turbulent flow without iteration.